The \(\Lambda \) , which is the lightest hyperon that contains an \(s\)  quark,
is more difficult to study than the nucleon because of its smaller
production cross section.
It was measured previously by the DM2 [1]} and
BaBar [2]} experiments, but with results were not conclusive.
BESIII has studied the channel \(e^+e^{-} \rightarrow \Lambda \bar{\Lambda }\)  [3]} with an analysis that used
a \(40.5~\mathrm {pb}^{-1}\)  data sample that was collected
at four different energy scan points during 2011 and 2012.
The lowest energy point is 2.2324 GeV, only 1 MeV
above the \(\Lambda \bar{\Lambda }\) -threshold.
These data made it possible to measure the Born cross section
very near threshold. To use the data as efficiently as possible,
both events where \(\Lambda \)  and \(\bar{\Lambda }\)  decayed to
the charged mode (\(\mathrm {Br}(\Lambda \rightarrow p\pi ^-) = 64\%\) )
and events where the \(\bar{\Lambda }\)  decayed to the neutral mode
(\(\mathrm {Br}(\bar{\Lambda } \rightarrow \bar{n} \pi ^0) = 36\%\) ) were
selected. In the first case, the identification relied on finding two
mono-energetic charged pions with evidence for a \(\bar{p}\) -annihilation
in the material of the beam pipe or the inner wall of the tracking chamber.
In the second case, the \(\bar{n}\) -annihilation was identified with a
multi-variate analysis of variables provided by the electromagnetic
calorimeter. Additonally, a mono-energetic \(\pi ^0\)  was reconstructed
to fully identify this decay channel.
For the higher energy points, only the charged decay modes of
\(\Lambda \)  and \(\bar{\Lambda }\)  were reconstructed by
identifying all the charged tracks and using the event kinematics.
The resulting measurement [3]} of the Born cross section
are shown in Fig. REF (a) together with previous
measurements [1]}, [2]}.
The Born cross section near threshold is found to be
\(312 \pm 51(\rm stat.) ^{+72}_{-45}\) (sys.) pb.
This result confirms BaBar's measurement [2]}
but with much higher momentum transfer squared accuracy.
Since the Coulomb factor is equal to 1 for neutral baryon pairs,
the cross section is expected to go to zero at threshold.
Therefore the observed threshold enhancement implies the existence
of a complicated underlying physics scenario.
The unexpected features of baryon pair production near threshold have driven
a lot of theoretical studies, including scenarios that invoke bound states
or unobserved meson resonances [8]}, [9]}, [10]}.
It was also interpreted as an attractive Coulomb interaction
on the constituent quark level [11]}, [12]}.
Another possible explanation is the final-state interactions which
play an important role near the threshold [13]}, [14]}, [15]}.
The BESIII measurement improves previous results at low invariant masses
at least by 10\(\%\)  and even more above 2.4 GeV/c.
The \(\Lambda \)  effective form factor extracted from
the cross section measurement is shown in Fig. REF (b).
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